1. Field of the Invention
The present invention relates to an image forming apparatus for forming image information onto, e.g., a transfer device by using, e.g., an electrophotographic system or the like.
2. Related Background Art
The applicant of the present invention has proposed a number of color image forming apparatuses for obtaining a full color image by arranging a plurality of image holding devices (photo sensitive drums or the like) in parallel {Japanese Unexamined Patent Publication (Kokai) No. 58-23074 and Japanese Unexamined Patent Publication (Kokai) No. 58-95361 (corresponding to U.S. Pat. No. 4,591,903), Japanese Unexamined Patent Publication (Kokai) No. 58-95362, Japanese Unexamined Patent Publication (Kokai) No. 58-154856, Japanese Unexamined Patent Publication (Kokai) No. 58-207021, and Japanese Unexamined Patent Publication (Kokai) No. 59-31976 (corresponding to U.S. patent application No. 521,832 applied on Aug. 10, 1983), Japanese Unexamined Patent Publication (Kokai) No. 59-46659, Japanese Unexamined Patent Publication (Kokai) No. 59-50460, Japanese Unexamined Patent Publication (Kokai) No. 59-42879, etc.}.
In the image forming apparatus of this type, an overlapping aberration (chromatic aberration) among respective colors at the time of the multitransfer becomes an extremely large problem.
To solve this problem, the applicant of the present invention has proposed methods for improving the chromatic aberration by a mechanical structure {Japanese Unexamined Patent Publication (Kokai) No. 59-155870, Japanese Unexamined Patent Publication (Kokai) No. 59-155869, Japanese Unexamined Patent Publication (Kokai) No. 59-155871, Japanese Unexamined Patent Publication (Kokai) No. 59-204069, Japanese Unexamined Patent Publication (Kokai) No. 59-155870, Japanese Unexamined Patent Publication (Kokai) No. 59-168467, and Japanese Unexamined Patent Publication (Kokai) No. 59-182139 (corresponding to U.S. Pat. No. 4,531,828), and Japanese Utility Model Application No. 62-12253 filed on Jan. 30, 1987}.
The chromatic aberration was fairly improved by these methods proposed. However, a problem still remains with regard to a point that the mechanical structure is stably moved within a range from 0.15 mm to 0.1 mm as an allowable difference of the chromatic aberration.
For example, finer slight instabilities such as stability in running of a belt, reproducibility of attachment/detachment of photo sensitive drums, and instabilities of the horizontal and vertical sinks in the case of an LBP (laser beam printer) newly appear as problems as the other technical elements are completed. On the other hand, with respect to the relations among the main unit, optical system, photo sensitive drums, and the like which have been once adjusted when the main unit was installed, if the shape of floor is not the same plane, a distortion occurs in the main unit due to, e.g., the movement of the main unit to another location or the like. In such a case, the very complicated and difficult adjustment must be again performed. On the other hand, the misregistration which is caused by the thermal expansion based on a change in room temperature of the main unit cannot be ignored in the high accurate printer.
In addition, methods whereby the image forming timing is individually adjusted every color have already been proposed {Japanese Unexamined Patent Publication (Kokai) No. 59-163971, (corresponding to U.S. Pat. No. 4,660,077) and Japanese Unexamined Patent Publication (Kokai) No. 58-226559}. On one hand, methods whereby an amount of chromatic aberration on an image is measured have also already been proposed {Japanese Unexamined Patent Publication (Kokai) No. 52-2604, Japanese Unexamined Patent Publication (Kokai) No. 53-21605, Japanese Unexamined Patent Publication (Kokai) No. 53-49514, Japanese Unexamined Patent Publication (Kokai) No. 56-157367, and Japanese Unexamined Patent Publication (Kokai) No. 58-14752}.
However, none of these methods proposed an organic system such that an amount of chromatic aberration detected is fed back to writing means. Therefore, it is the present situation such that the apparatus which can highly accurately improve the chromatic aberration is not proposed yet.